Use Case

Imagine you’re making a time based search engine for movies and/or events. Because your data will span many timezones, you decide that all dates & times should be stored on the server as UTC. This pushes local timezone conversion to the client side, where it belongs, simplifying the server side data structures and search operations. You want your search engine to be AJAX enabled, but you don’t like XML because it’s so verbose, so you go with JSON for serialization. You also want users to be able to input their own range based queries without being forced to use specific datetime formats. Leaving out all the hard stuff, the above snippets can be used for communication between a django webapp and a time based search engine.

Datejs

Datejs, being javascript, is designed for parsing and creating human readable dates & times. It’s powerful parse() function can handle all the dates & times you’d expect, plus fuzzier human readable date words. Here are some examples from their site.

And if you are programmatically creating Date objects, here’s a few functions I find myself using frequently.

// get a new Date object set to local date
var dt = Date.today();
// get that same Date object set to current time
var dt = Date.today().setTimeToNow();
// set the local time to 10:30 AM
var dt = Date.today().set({hour: 10, minute: 30});
// produce an ISO formatted datetime string converted to UTC
dt.toISOString();

python-dateutil

Like Datejs, dateutil also has a powerful parse() function. While it can’t handle words like “today” or “tomorrow”, it can handle nearly every (American) date format that exists. Here’s a few examples.

An option that comes especially in handy is to pass in fuzzy=True. This tells parse() to ignore unknown tokens while parsing. This next example would raise a ValueError without fuzzy=True.

>>> parser.parse("Thurs, 4/2/09 09:00 PM", fuzzy=True)

It don’t know how well it works for international date formats, but parse() does have options for reading days first and years first, so I’m guessing it can be made to work.

dateutil also provides some great timezone support. I’ve always been surprised at python’s lack of concrete tzinfo classes, but dateutil.tz more than makes up for it (there’s also pytz, but I haven’t figured out why I need it instead of or in addition to dateutil.tz). Here’s a function for parsing a string and returning a UTC datetime object.

dateutil does a lot more than provide tzinfo objects and parse datetimes; it can also calculate relative deltas and handle iCal recurrence rules. I’m sure a whole calendar application could be built based on dateutil, but my interest is in parsing and converting datetimes to and from UTC, and in that respect dateutil excels.